Electromagnetically actuated control valves are widely used in fuel injectors and timing fluid and injection fuel metering system for precisely controlling the timing and metering of the injection fuel and timing fluid. Precise control of the timing and metering of fuel and timing fluid is necessary to achieve maximum efficiency of the fuel system of an internal combustion engine. In addition, valve designers continually attempt to reduce the size of the control valves to reduce the overall size and weight of the engine and permit the control valves to be easily mounted in a variety of locations on the engine without exceeding packaging restraints.
Another concern of valve designers is valve seat wear and valve bounce. Control valves are often operated by a solenoid type actuator assembly. The response time of the valve assembly has been decreased by improving the de-energizing response time of the actuator. However, as a result, the valve element closing velocity is increased resulting in increased impact forces on the valve seat. These high impact forces of the valve element against a valve seat cause excessive seat stresses, valve seat beating and excessive wear. Moreover, when the valve impacts the valve seat at a high velocity, the valve tends to bounce off the seat adversely affecting the control of fluid flow and causing additional valve seat wear.
U.S. Pat. No. 5,626,325 discloses a valve assembly designed to reduce valve seat beating. Specifically, the valve assembly includes a compliant web supporting the valve seat to provide a flexing motion when the valve element seats against the valve seat thereby mitigating seat beating. However, this design may not sufficiently reduce valve seat stresses. Also, the movement of the valve seat may undesirably increase valve bounce and interfere with valve sealing.
U.S. Pat. No. 4,765,587 discloses two embodiments of a solenoid valve that reduces the impact force of a valve poppet on a valve seat. The first embodiment discloses a solenoid valve that decouples an armature from a poppet as the poppet impacts a valve seat, thereby reducing seat impact stresses. When an actuator coil is de-energized, a return spring urges the poppet and the armature to move toward the valve seat surface. When the poppet impacts the seat surface, the armature decouples from the poppet and travels an additional distance before abutting a body surface. However, the armature remains separated from the poppet until the next cycle when the energized coil pulls the armature away from the body surface causing it to link with the poppet. This delay in the movement of the poppet upon actuation of the actuator creates an undesirable delay in valve response. Also, the relatively soft armature directly contacts the poppet and the housing thereby possibly causing excessive degradation of the armature.
The second embodiment (FIG. 4) of U.S. Pat. No. 4,765,587 discloses a solenoid valve design utilizing two opposing springs to reduce the pressure on a valve seat when a coil is de-energized. In operation, as the coil is de-energized, a return spring urges an armature and plunger to move toward the valve seat. The spacing between the various parts is such that the valve engages the seat before the armature completes its cycle. The additional force exerted on the valve seat as the armature completes its cycle is absorbed by one of the opposing springs. When energized, the coil urges the armature and plunger away from the valve seat. The return spring is connected to the armature which in turn is linked to the plunger via two continuously compressed opposing springs. This configuration appears to result in the valve remaining in contact with the valve seat for a longer period of time after the coil is energized than if the return spring was connected directly to the plunger. However, again, the armature remains separated from the plunger upon closing of the valve.
Consequently, there is a need for a compact, inexpensive valve assembly capable of effectively controlling valve movement throughout all valve operating conditions while minimizing valve seat stresses.